A great number of photographic processes have heretofore been known wherein development of the exposed film unit is accomplished by applying to the exposed film unit a processing composition including a viscosity-increasing reagent to facilitate spreading of the composition, e.g., a film-forming material such as hydroxyethyl cellulose or carboxymethyl cellulose, etc., high molecular weight polymers which form a relatively firm and stable film.
Typical of such known processes are silver diffusion transfer systems for forming a transfer image (usually a "positive") in silver; and color diffusion transfer systems wherein a dye transfer image (also usually a "positive") is formed.
In a conventional silver diffusion transfer system of the foregoing description, an exposed silver halide layer containing a developable image is developed by applying a viscous processing composition, typically an aqueous alkaline composition including a silver halide developing agent and a silver halide solvent, to develop the exposed silver halide and as a function thereof to form an imagewise distribution of a soluble silver complex which is transferred at least in part, to form a positive black-and-white image in silver.
Color transfer images are typically formed by exposing a photosensitive element including at least one light-sensitive silver halide layer having a dye image-providing material associated therewith, contacting the thus exposed element with a viscous processing composition, usually an aqueous alkaline composition, to develop the exposed photosensitive element and as a function thereof providing a differential in solubility or diffusibility of the associated dye image-providing material, thus providing an imagewise distribution of more soluble or diffusible dye image-providing material which is then transferred to a dyeable stratum to impart thereto a dye transfer image. The dyeable stratum may be contained on the photosensitive element or on a separate element referred to as an image-receiving element. Dye image-providing materials employed in these color processes generally may be characterized as either (1) initially soluble or diffusible in the processing composition but are selectively rendered non-diffusible in an imagewise pattern as a function of development; or (2) initially insoluble or non-diffusible in the processing composition but which are selectively rendered diffusible in an imagewise pattern as a function of development. These materials may be complete dyes or dye intermediates, e.g., color couplers.
As examples of initially soluble or diffusible materials and their application in color diffusion transfer, mention may be made of those disclosed, for example, in U.S. Pat. Nos. 2,647,049; 2,661,293; 2,698,244; 2,698,798; 2,802,735; 2,774,668 and 2,983,606. As examples of initially non-diffusible materials and their use in color transfer systems, mention may be made of the materials and systems disclosed in U.S. Pat. Nos. 3,443,939; 3,443,940; 3,227,550; 3,227,551; 3,227,552; 3,227,554; 3,243,294; and 3,445,228.
In any of these color systems, multicolor images may be obtained by employing a film unit containing at least two selectively sensitized silver halide layers each having associated therewith a dye image-providing material exhibiting desired spectral absorption characteristics. The most commonly employed elements of this type are the so-called tripack structures employing a blue-, a green- and a red-sensitive silver halide layer having associated therewith, respectively, a yellow, a magenta and a cyan dye image-providing material.
The foregoing description is illustrative of the various kinds of photographic systems heretofore known which employ viscous processing reagents. Such systems include both black- and white and color, reflection prints and transparencies, so-called peel apart systems wherein the receiving element containing the image is separated from the negative element, and so-called integral systems wherein the respective elements are retained together subsequent to image formation.
Many materials have previously been suggested for use as the viscosity-increasing agent. For example, U.S. Pat. Nos. 2,543,181; 2,558,857; 2,616,807; 2,662,822; 2,983,606; 3,415,644; 3,594,164; 3,594,165 and others mention the use of such materials as sodium carboxymethyl cellulose, hydroxyethyl cellulose, sodium alginate, certain starches and gums, and the like. Many additional patents are directed to various problems with such viscous processing reagents. For instance, U.S. Pat. No. 3,362,822 is directed to the addition of a polymeric substance which is soluble in the alkaline composition but precipitates at a lower pH of 7-11, e.g. a polymeric acid having an ionization constant between about 10.sup.-6 and 10.sup.-12, in order to accelerate the setting time of the layer of processing composition; U.S. Pat. No. 3,390,990 relates to the use of a cross-linking agent for the polymeric viscosity-increasing reagent in order to obtain denser transfer images along with a reduction in the amount of viscosity-increasing compound; U.S. Pat. No. 3,776,726 describes and claims the addition of colloidal silica to increase the viscosity, etc.